U.S. patent number 7,108,349 [Application Number 11/135,136] was granted by the patent office on 2006-09-19 for print head charge shield.
This patent grant is currently assigned to Hewlett-Packard Development Company, L.P.. Invention is credited to Sam Sarmast, Wen-Li Su.
United States Patent |
7,108,349 |
Sarmast , et al. |
September 19, 2006 |
Print head charge shield
Abstract
A printer according to the present techniques includes a print
head having at least one nozzle for ejecting an ink drop and a
sensing element for detecting the ink drop. The print head includes
a charge shield for imparting an electrical charge into the ink
drop during ejection from the nozzle and for shielding electrical
noise generated in the print head.
Inventors: |
Sarmast; Sam (Vancouver,
WA), Su; Wen-Li (Vancouver, WA) |
Assignee: |
Hewlett-Packard Development
Company, L.P. (Houston, TX)
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Family
ID: |
32230160 |
Appl.
No.: |
11/135,136 |
Filed: |
May 23, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050212848 A1 |
Sep 29, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10411048 |
Apr 9, 2003 |
6951379 |
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Current U.S.
Class: |
347/19 |
Current CPC
Class: |
B41J
2/085 (20130101); B41J 2/12 (20130101); B41J
2/125 (20130101); B41J 2/1753 (20130101) |
Current International
Class: |
B41J
29/393 (20060101) |
Field of
Search: |
;347/19 |
Primary Examiner: Meier; Stephen
Assistant Examiner: Huffman; Julian D.
Parent Case Text
This application is a continuation of application Ser. No.
10/411,048 filed on Apr. 9, 2003 now U.S. Pat. No. 6,951,379.
Claims
What is claimed is:
1. A method for drop detection, comprising: detecting an ink drop
fired from a nozzle of a print head; shielding an electrical noise
generated by a firing mechanism in the print head by attaching a
charge shield to the print head that both shields the electrical
noise and imparts a charge onto the ink drop.
2. The method of claim 1, wherein shielding comprises shielding
electrical noise generated in the print head from a sensing element
for the ink drop.
3. A method for drop detection, comprising: detecting an ink drop
fired from a nozzle of a print head; shielding electrical noise
generated in the print head from firing the ink drop by providing
the print head with a charge shield that both shields the
electrical noise and imparts a charge onto the ink drop wherein the
charge shield is integrated into a flexible cable attached to the
print head.
4. An apparatus for drop detection, comprising: means for detecting
an ink drop fired from a nozzle of a print head; means for
shielding an electrical noise generated by a firing mechanism in
the print head comprising a charge shield attached to the print
head that both shields the electrical noise and imparts a charge
onto the ink drop.
5. The apparatus of claim 4, wherein the means for shielding
comprises means for shielding electrical noise generated in the
print head from a sensing element for the ink drop.
6. An apparatus for drop detection, comprising: means for detecting
an ink drop fired from a nozzle of a print head; means for
shielding electrical noise generated in the print head from firing
the ink drop comprising a charge shield that both shields the
electrical noise and imparts a charge onto the ink drop wherein the
charge shield is integrated into a flexible cable attached to the
print head.
Description
BACKGROUND
A typical printer includes one or more print heads for applying ink
onto paper. A typical print head includes a set of nozzles and a
firing mechanism for ejecting ink drops through the nozzles.
Examples of firing mechanisms include piezo-electric crystals that
squeeze out ink drops through the nozzles and heating elements that
boil out ink drops through the nozzles.
It is often desirable to provide a printer with an ink drop
detector. An ink drop detector may be used to detect whether ink
drops are being ejected from individual nozzles of a print head.
For example, an ink drop detector may be used to determine whether
nozzles are clogged and would benefit from cleaning or whether
individual nozzles have failed permanently.
One type of prior ink drop detector that may be employed in
printers is an electrostatic drop detector. An electrostatic drop
detector may include a conductive surface that functions as a
charging element and a sensing element. A print head may be
positioned to fire ink drops at the conductive surface. A high
voltage may be applied to the conductive surface to create a
relatively strong electric field that induces an electrical charge
into the ink drops ejected from the print head. The charged ink
drops that strike the conductive surface usually impart an
electrical pulse into the conductive surface. Signal processing may
be used to derive a drop detection indicator from the electrical
pulses imparted by the charged ink drops onto the conductive
surface.
The firing mechanism in a typical prior print head may create
electrical noise that coincides with ink drop ejection. The
electrical noise caused by firing pulses in a print head may be
mistaken for charged ink drops by the electrostatic drop detector
and give false indications of ink drop ejection.
In addition, the electrical noise caused by firing pulses in a
print head may increase the signal-to-noise ratio which leads to
more expensive detection circuitry and more complex signal
processing.
SUMMARY OF THE INVENTION
A printer according to the present techniques includes a print head
having at least one nozzle for ejecting an ink drop and a sensing
element for detecting the ink drop. The print head includes a
charge shield for imparting an electrical charge into the ink drop
during ejection from the nozzle and for shielding electrical noise
generated in the print head. The charge shield in the print head
increases the charge induced into the ink drop while shielding the
separate sensing element from electrical noise.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention is described with respect to particular
exemplary embodiments thereof and reference is accordingly made to
the drawings in which:
FIG. 1 shows a print head that includes a charge shield according
to the present techniques;
FIG. 2 shows another embodiment of a print head according to the
present techniques;
FIG. 3 shows yet another embodiment of a print head according to
the present techniques;
FIG. 4 shows another embodiment of a charge shield according to the
present techniques;
FIG. 5 shows a printer that incorporates electrostatic drop
detection according to the present teachings.
DETAILED DESCRIPTION
FIG. 1 shows a print head 10 that includes a charge shield 30
according to the present techniques. The print head 10 includes a
set of nozzles 32 and a firing mechanism for ejecting ink drops
from the nozzles 32. The ink drops ejected from the nozzles 32
strike a sensing element 14. The charge shield 30 in this
embodiment is mounted on the print head 10.
The charge shield 30 is applied with a high voltage by a high
voltage generator 24. The high voltage on the charge shield 30
imparts an electrical charge into the ink drops ejected from the
nozzles 32. Each charged ink drop that strikes the sensing element
14 imparts an electrical pulse into the sensing element 14. The
electrical pulses imparted into the sensing element 14 are
amplified by a sense amplifier 16 to provide detection signal
70.
The charge shield 30 provides an AC path to ground for shielding
electrical noise that may be generated in the print head 10. For
example, electrical noise may be generated by the ink drop firing
mechanism in the print head 10. The AC path to ground provided by
the charge shield 30 reduces the electrical noise in the print head
10 that would otherwise reach the sensing element 14 and influence
the electrical state of the sensing element 14. For example, the
charge shield 30 attenuates firing noise in the print head 10,
thereby reduoing the magnitude of pulses in the sensing element 14
that can be mistaken for an ink drop from a clogged nozzle.
The charge shield 30 may be a conductive metal plate, a metal foil,
a copper tape, etc.
The charge shield 30 may be mounted on the print head 10 using, for
example, an adhesive, fasteners, etc. Alternatively, the charge
shield 30 may be mounted on a carriage for the print head 10.
FIG. 2 shows another embodiment of the print head 10 according to
the present techniques. The print head 10 in this embodiment
includes a flexible ribbon cable that includes two layers--a layer
40 and a layer 42. The layer 42 in the region near the nozzles 32
holds a charge shield that charges the ink drops ejected from the
nozzles 32 and that shields the electrical noise generated in the
print head 10. The charge shield may be disposed on either the
upper or lower surface of the layer 42 or may be contained within
the layer 42. The layer 42 also includes a set electrical signal
lines for applying a high voltage to the charge shield. The layer
40 provides data signals to a set of electrical contacts 44 of the
print head 10.
FIG. 3 shows yet another embodiment of the print head 10 according
to the present techniques. The print head 10 in this embodiment
includes a silicon structure 50 that includes electrical elements
for firing the nozzles 32. For example, the silicon structure 50
may include thermal heating elements and associated drive
electronics for firing individual heating elements. In this
embodiment, the charge shield is incorporated into the silicon
structure 50.
FIG. 4 shows another embodiment of the charge shield 30 according
to the present techniques. The charge shield 30 in this embodiment
encompasses the range of movement of a carriage 210 across a paper
200. The carriage 210 includes a set of print heads 220 each having
nozzles for ejecting ink drops onto the paper 200 through an
opening 230 in the charge shield 30. The sensing element 14 in this
embodiment also encompasses the range of the movement of the
carriage 210.
The high voltage electronics for the charge shield in any of the
above embodiments may be integrated into an analog ASIC on the
carriage for the print head 10.
FIG. 5 shows a printer 100 that incorporates electrostatic drop
detection according to the present teachings. The print head 10 is
shown positioned opposite the sensing element 14 at a distance of
several millimeters during an ink drop detection cycle. The sensing
element 14 may be disposed in an existing service station in the
printer 100. The charge shield in the print head 10 is supplied
with a voltage potential V0 by the high voltage generator 24. The
voltage potential V0 may be a DC voltage or an AC voltage. A drive
voltage V.sub.DRIVE is applied for actuating the ink drop firing
mechanisms in the print head 10. The voltage potential V.sub.DRIVE
is relatively low compared to V0. For example, in one embodiment,
V.sub.DRIVE is approximately 5 volts and the high voltage generator
24 applies a V0 of approximately 100 volts. The high voltage V0
creates in a relatively high electric field near the nozzles 32 of
the print head 10, i.e. at the location of the charge shield in the
print head 10.
The print head 10 ejects a series of ink drops 12 during an ink
drop detection cycle. The relatively high electric field near the
nozzles of the print head 10 causes the accumulation of electrical
charge in the ink drops 12 as they shear away from a nozzle of the
print head 10. As each of the ink drops 12 separates from the print
head 10 it retains its accumulated electrical charge. Each of the
ink drops 12 transports its induced charge to the sensing element
14.
Each of the charged ink drops 12 imparts a spike or pulse of
electrical charge onto the sensing element 14 as it makes contact.
These spikes or pulses on the sensing element 14 are coupled to an
input of the sense amplifier 16. The sense amplifier 16 amplifies
the pulses and provides filtering.
In one embodiment, the ink drops 12 are fired in a series of bursts
having a predetermined frequency or pattern of frequencies. The
sense amplifier 16 is tuned to amplify signals from the sensing
element 14 at the frequency or frequencies of the predetermined
pattern. The detection signal 70 from the sense amplifier 16 is
provided to an analog-to-digital converter 18 which generates a
digitized version. This digitized version of the detection signal
70 is provided to the printer processor 20 which executes signal
processing code 62.
The printer processor 20 when executing the signal processing code
62 performs a digital signal processing function on the digitized
version of the detection signal 70. The digital signal processing
function performed by the printer processor 20 provides a drop
detection value that is then used to characterize ink drops ejected
from the print head 10 during an ink drop detection cycle. One
characteristic which the drop detection value is used to determine
is whether any ink drops were ejected during the ink drop detection
cycle.
The drop detection value generated by the print processor 20 is
proportional to the number of drops fired from the print head 10.
The drop detection value is also proportional to the volume of the
ink drops ejected and the velocity of the ink drops that were
ejected.
The printer processor 20 compares the drop detection value or
values obtained from a ink drop detection cycle to a stored
representation of drop detection values to determine the number of
drops fired by the print head 10 during the ink drop detection
cycle. For example, if the drop detection value from an ink drop
detection cycle is within a tolerance value of a stored drop
detection value corresponding to N ink drops, then it can be
concluded that N ink drops struck the sensing element 14 during
bursts of a detection cycle. If the drive control electronics for
the print head 10 actuated N firings per burst then it can be
concluded that the particular nozzle of the print head 10 under
test is functioning properly. If, on the other hand, the drive
control electronics actuated N firings and the resulting drop
detection value is significantly below the stored drop detection
value corresponding to N ink drops then it can be concluded that
the particular nozzle under test is not functioning properly.
The drop detection values determined by the printer processor 20
may be used for rendering a go/no-go decision on each of the
nozzles in the print head 10. In one embodiment, the printer
processor 20 tests a few nozzles on the fly at the end of a print
cycle on a page. If the drop detection value from a particular ink
drop detection cycle is too low then the printer 100 may apply the
print head 10 to the service station in the printer. If after
cleaning several times the particular nozzle or nozzles are still
bad then the printer processor 20 may adjust its printing algorithm
embodied in the printing codes 60 to compensate for the bad nozzle
or provide an error indication to a user of the printer that the
print head 10 should be replaced.
The drop detection values may be used for characterizing the
individual nozzles of the print head 10 in order to enhance gray
scale or color resolution. The drop detection value may be used for
adjusting the drive voltages to individual ones or groups of
nozzles in a thermal print head in order to enhance the life of the
heating elements contained therein.
The sensing element 14 may be contained in a trough or spittoon
that accepts test ink drops fired from the print head 10. The sense
amplifier 16 may be may be implemented in an application specific
integrated circuit that is encapsulated by an insulating layer in
the spittoon. The sensing element 14 may be a metal layer disposed
on top of the insulating layer. Alternatively, the sensing element
14 may be positioned beneath a paper path in a printing area
opposite the print head 10 and may be constructed of a conductive
pad of foam or a metallic or a conductive plastic member.
The foregoing detailed description is provided for the purposes of
illustration and is not intended to be exhaustive or to limit the
invention to the precise embodiment disclosed. Accordingly, the
scope of the present invention is defined by the appended
claims.
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